Co-abelian toroidal compactifications of torsion free ball quotients

Abstract

Let X' be the toroidal compactification of the quotient of the complex 2-ball by a torsion free lattice G of SU(2,1). We say that X'is co-abelian if there is an abelian surface, birational to X'. The present work can be viewed as an illustration for the presence of a plenty of non-compact co-abelian torsion free toroidal compactifications. More precisely, it shows that all the admissible values for the volume of a torsion free quotient of the complex 2-ball are attained by co-abelian Picard modular ones over Eisenstein numbers. The article provides three types of infinite series of finite unramified coverings of co-abelian, torsion free, Picard modular toroidal compactifications over Eisenstein numbers, with infinitely increasing volumes. The first type is supported by mutually birational members with fixed number of cusps. The second kind is with mutually birational terms and infinitely increasing number of cusps. The third kind of series relates mutually non-birational toroidal compactifications with infinitely increasing number of cusps.